Few molecules of demonstrated therapeutic value can be transported through the skin, even with the use of approved chemical enhancers. The main barrier to transport of molecules through the skin is the stratum corneum (the outermost layer of the skin).
Devices including arrays of relatively small structures, sometimes referred to as microneedles or micro-pins, have been disclosed for use in connection with the delivery of therapeutic agents and other substances through the skin and other surfaces. The devices are typically pressed against the skin in an effort to pierce the stratum corneum such that the therapeutic agents and other substances can pass through that layer and into the tissues below.
Issues associated with microneedle devices include the ability to effectively pierce the stratum corneum. That ability can be compromised by the desire to limit the height of the microneedle structures to avoid stimulating the nerves located under the stratum corneum. As a result of the limited height of the structures, it may be difficult to reliably pierce the stratum corneum in enough locations to effectively deliver a therapeutic agent to a patient.
Another issue associated with known microneedle devices is the structural integrity of the microneedle structures themselves. Structures that are not robust may fracture or otherwise degrade when advanced through the stratum corneum. As a result, portions of the structures may be left imbedded in the skin. Although the structures are typically manufactured of biologically inert materials, it may be preferred that no portions of the structure remain in the skin after use.